CHICKEN is a compiler for the Scheme programming language. It produces portable and efficient C and supports the R5RS and R7RS (work in progress) standards, and many extensions. It runs on Linux, OS X, Windows, many Unix flavours, and aims to be...

Free

Distributed free for use and modification under the BSD License (freedom to user and developer).

Simple

Lightweight on dependencies (a C toolchain and GNU Make) and easy to install.

Portable

Runs on many platforms, including x86, x86-64, ARM, MIPS, SPARC64 and PowerPC.

Extensible

Many libraries and extensions are available at Eggs Unlimited and new ones can be easily created.